Combustion – Flame holder having protective flame enclosing or flame... – Including means feeding air axially spaced points of the flame
Patent
1980-04-30
1982-12-07
Scott, Samuel
Combustion
Flame holder having protective flame enclosing or flame...
Including means feeding air axially spaced points of the flame
431353, 60757, 60760, 432223, 110212, F23G 706
Patent
active
043625002
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a unit for combustion of process gases and the production of hot air, directly usable for drying, with the aid of supplementary fuel in the form of gas, light-oil or heavy-oil, the combustion chamber itself being so constructed that it can be adapted to a selected supplementary fuel.
The unit according to the invention is a sheet metal construction and the use of sheet metal in the combustion chamber is made possible by the specific cooling technique and the mixing technique in the unit. The use of a metal construction provides an exceptional controllability and a great savings in energy in the unit, since there are no heavy walled-in constructions with high heat capacity to be cooled or heated when settings are changed, and the unit can be started or stopped almost instantaneously. Thus the construction according to the invention weighs only a small fraction of what the corresponding traditional construction with ceramic walling-in would do.
Our construction is such that it can easily be adapted to different supplementary fuels depending on what is most suited to different plants and processes, and it can also be used for heavy-oil, which up to now it has been difficult to burn in sheet metal burners.
The reason for the difficulty of using heavy-oil in sheet metal construction, and for the limited usability of lighter fuels, is the low durability. To obtain a complete and soot-free combustion, the temperature must be kept high. This subjects the material in the combustion chamber to great stresses. Up to now, in order to obtain sufficiently durable material, it has been necessary to use ceramic material, e.g. refractory brick. The problems which are significant in a sheet metal construction using such fuels as gas and light-oil, are further aggravated when using heavy-oil. The pollutants in heavy oil, especially the small amounts of vanadium and sodium, form an easily melted slag which sticks to the wall of the combustion chamber and can cause corrosion even at 550.degree. C. It has previously not been possible to combine the features of complete combustion and low wall temperature.
By using specific grades of steel, e.g. Avesta 253 MA and Inconel Alloy 671 and a special design technology in the construction, for example in parts subjected to high temperatures, we have achieved a very good life-time for our units. As an example it can be mentioned that in a flanged pipe connection the weld cannot be made in the usual manner with an annular flange welded onto a pipe. Rather, a flange with an extended nose must be used and the pipe welded to this flange nose to provide a more gradual transition between flange and pipe.
To obtain a satisfactory incineration of the organic compounds in the process gases the temperature must usually be kept at about 800.degree. C. It is true that special heat resistant organic compounds require temperatures as high as 1300.degree.-1400.degree. C., but these are exceptional cases requiring exceptional measures which we will not deal with here. The temperature of the wall of the combustion chamber may not exceed about 550.degree. C. since otherwise there would be especially serious corrosion when heavy-oil is used. In order to clarify the situation, we will mention something of the combustion process.
The heat to which the wall of the combustion chamber is subjected is made up of a convective portion and a radiant portion. While the gaseous fuels and the lighter distilled oil products contribute insignificant or small amounts of radiant heat, the heavy-oil, because of the large particle content in the flame, subjects the wall to much more radiant heat.
The radiant heat from the flame follows Stefan-Bolzmann's Law, i.e. it is equal to .lambda..times.T.sup.4 where .lambda. is a function of, inter alia, the coefficient of emission which for natural gas is about 0.1, for light-oil about 0.25 and for heavy-oil about 0.45, i.e. almost five times as great as for the gas.
The incoming process gas is preheated by leading it along the outside of the combus
REFERENCES:
patent: 2446059 (1948-07-01), Peterson et al.
patent: 2458497 (1949-01-01), Bailey
patent: 3414362 (1968-12-01), Schoppe
patent: 3940253 (1976-02-01), Zetterstrom
patent: 4038032 (1977-07-01), Brewer et al.
patent: 4054028 (1977-10-01), Kawaguchi
Andersson John O.
Eriksson Torsten L.
Nystrom Olle
Barrett Lee E.
Scott Samuel
Volvo Flygmotor AB
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